The present invention relates to the commercial processing of poultry, fowl and seafood and, more particularly, to a method of increasing the shelf life of such commercially processed products. In more detail, the present invention relates to a new application for hydrogen peroxide to extend the shelf life of commercially processed foods of the type described herein. Specifically, the herein described invention relates to efforts conducted to extend the customary commercial shelf life of the various animals processed in commercial slaughtering plants.
Poultry, other fowl and fish (e.g. chicken, turkey, duck, geese, catfish, trout, shrimp and salmon, etc.) are processed in commercial slaughtering plants in a similar way. The final treatment step is the chilling of the processed carcass or meat to a suitable temperature, possibly in the range of 36.degree.-42.degree. F. This is accomplished by using a mixture of water and ice in a so-called chiller. As is known in the art, a commercial chiller is usually a stainless steel tank where the processed carcass or meat is immersed into the water/ice mixture, moved through it by mechanical means and retrieved at the other end. The retention time depends on the type of animal processed. For example, the time for chickens is between thirty and sixty minutes, for catfish it is between twenty and fifty minutes. These periods of time have been established through actual commercial practices and can be varied depending on surrounding conditions as will be apparent to those skilled in the art.
The average amount of water used per carcass or meat also depends on the type of animal processed; e.g. for chickens it is approximately 0.5 gallons of chiller water per carcass, for turkey it is approximately 0.8 gallons of chiller water per carcass and for catfish meat it is generally between 0.3 and 1 gallon of water per piece. Based on actual commercial operations over the years, these amounts of water have been found to be satisfactory to achieve the intended purpose. As with all such processing conditions, the precise values can change depending on overall conditions.
To accomplish an even temperature distribution in the chiller, the water is agitated with compressed air or by mechanical devices. To control bacterial cross-contamination, in the past and even at present, chlorine is used in the chiller water. Chlorine levels vary for the different animals processed, but is usually between 10 and 70 ppm. In spite of the chlorine used, there are still a significant number of micro-organisms (up to 10.sup.8) on the processed carcasses or meat. Chlorine is, of course, an environmentally hazardous material and is undesirable to have in contact with food and people.
The remaining bacterial contamination on the processed animal has a strong impact on the achievable shelf life. Assuming ideal storage and transportation conditions, the shelf life of chicken and turkey is between ten and twenty days, with the industry average being fifteen days. For processed catfish, the shelf life usually achieved is ten to fifteen days, with the industry average being twelve days.
Hydrogen peroxide (H.sub.2 O.sub.2) was first evaluated by the applicants to eliminate salmonella organisms from processed poultry and other fowl. A concentration of 0.1% H.sub.2 O.sub.2 was used to eliminate all salmonella organisms in a substrate petri dish. Utilizing the same concentration of H.sub.2 O.sub.2 under chiller water conditions brought no reduction in salmonella. After increasing the concentration to 1%, a 50-60% reduction in salmonella under processing conditions was obtained. The analysis of the poultry and fowl so treated was carried out using ground pieces of the breast feather tray and a DNA probe, which the art recognizes as representing the most stringent test method available for salmonella. The treated birds were severely bleached and the skin was partially damaged. The areas of the neck and the vent opening were especially effected. The same effects were reported by H. S. Lillard and J. E. Yhompson in volume 48 of the Journal of Food Science, 1983. Beyond the detrimental effects of hydrogen peroxide to the poultry carcasses at this concentration, it was noted that all of the undesirable side effects disappeared after storing the carcasses one day at refrigeration temperature. These effects were previously reported by Mulder, van der Hulst and Bolder in a publication of the Journal of Poultry Science, volume 66, 1987.
The poor efficacy of the high concentration of H.sub.2 O.sub.2 versus the excellent results obtained in the petri dish can be explained by the hydrophobic and hydrophilic conditions between the poultry skin and the chiller water during commercial processing. The fatty surface of the poultry carcass does not allow sufficient contact between the H.sub.2 O.sub.2 and the actual skin surface to which the bacteria are attached. The same holds true for all commercially processed fowl and was reconfirmed for commercially processed fish. A publication from H. S. Lillard in volume 53 of the Journal of Food Science, 1988, further explains the mechanism by which salmonella attaches to poultry skin and muscles, and outlines the possibility that some microorganisms are entrapped in the skin pores or exposed tissue. Nevertheless, there were indications that the use of surfactants could be of help in controlling salmonella attachment to the skin. The effect of surfactants on the control of salmonella on poultry carcasses was described by James C. Hill and Frank Ivey in U.S. Pat. No. 4,770,884, dated Sep. 13, 1988. The patent describes the use of various surfactants at a pH of about 4 and a temperature between 0.degree. and 60.degree. C., at a concentration of 50 to 400 ppm.
At the recommended treatment level of up to 400 ppm of the surfactant, and the relatively low pH, tests showed that these measures will interfere with the taste and texture of the bird. At the higher doses of the recommended surfactant poultry meat had a "soapy" taste. The fish meat also acquired the same taste at levels slightly below 100 ppm. The reduced pH of the chiller water, adjusted with phosphoric acid, undesirably changed the texture of the meat. After preparation, the meat was not as tender as the untreated carcasses. These effects can be explained by the absorption effect which takes place when the carcass or meat is immersed in the chiller water. During the chilling process, the carcass will lose most of the blood remaining in the tissue and absorb water in an amount of up to 6% of its weight. Manipulation of the pH level of the water and additives easily alters the taste and texture of the meat so treated. Even the process based on sodium percarbonate and hydrogen peroxide, as described in U.S. Pat. No. 4,683,618, dated Aug. 4, 1987, of Gerard T. O'Brien, interferes with the taste and the texture of the carcass so treated. Based on the mode of application, it is suspected that the sodium carbonate, which increases the pH, changes the poultry meat's taste and texture. Tests to determine the TVA factor, which would indicate the oxidative effect of the 3% hydrogen peroxide, provided inconclusive results, but did indicate problems associated with the exposure of a poultry carcass to 3% hydrogen peroxide for a short period of time.